The objective of this proposal is to test the hypothesis that the beta- carotene status of breast tissue can modulate breast cancer, either directly or through the formation of metabolites such as retinoic acid. This hypothesis arises out of the very strong observational epidemiological evidence, both with respect to diet and serum concentrations, indicating that carotenoids in general, and beta-carotene in particular, are associated with a decreased risk of various types cancer, including breast cancer. In addition, more than two decades of clinical experience has demonstrated that the administration of high doses of beta-carotene (up to 300 mg/d) for extended periods of time has not resulted in toxic side effects. However, the recently reported ATBC study carried out in Finland, which reported evidence that the administration of 20 mg/d beta-carotene resulted in an increased mortality from lung cancer in a large cohort of adult male smokers, has raised the question of safety. We should wait for the results of additional intervention studies before concluding that there is a safety issue with beta-carotene. The accumulated data that the major metabolic products of carotenoids (the retinoids, and retinoic acid in particular) are effective anticancer agents, although associated with high risks of side-effects, indicate that understanding the process whereby beta-carotene is metabolized to retinoic acid is an important area of investigation. Our laboratories have been instrumental in documenting, both in vitro and in vivo, that beta-carotene is metabolized at several double bonds, yielding apocarotenoids as well as retinoic acid. These experiments have been carried out using the all-trans isomer of beta-carotene, but with the identification of 9-cis-retinoic acid as the specific ligand for the nuclear receptor, RXR, the question arises as to the source of 9-cis-retinoic acid in the body. We propose studying both all-trans and 9-cis beta-carotene metabolism in normal and cancerous human breast tissue to determine if differences exist. Our specific aims are to: 1. Determine the levels of beta-carotene and other carotenoids, as well as retinoic acid, and other retinoids, in both cancerous tissues and normal human breast epithelium of women with breast cancer, and in non-cancerous tissues of women without breast cancer. 2. Determine the metabolism of beta-carotene to retinoic acid and other metabolites, in both cancerous and normal human breast epithelium. 3. Determine the effect of hormonal status on levels and metabolism of all- trans and 9-cis B-carotene in normal and cancerous breast tissues. In collaboration with Project I (Dr. Peacocke), our 4th specific aim is to determine whether short-term (10 d) supplementation with beta-carotene (45 mg/d) alters the levels of carotenoids and retinoids, as well as the expression of RARbeta2, in both normal and cancerous breast tissue. Dr. Monica Peacocke will serve as Program Coordinator for both proposals.